Ok, so I figured out I can enable other input languages through settings, which at least makes it easier to enter some special characters, but only the biggest languages have "Dictionary available". Is it possible to somehow add dictionaries for the other selectable input languages?
It looks like that all dictionaries are embedded into keyboards, but you can try to find the dictionary by searching in Android market with query:
Your_desired_language language pack
For example for "Finnish language pack" there are packs for 3 different keyboards: SlideIT, AnySoftKeyboard and Gingerbread keyboard (unfortunately not the original one, you should install Gingerbread keyboard app from market even if you already have original Gingerbread keyboard).